The present invention relates to aqueous, concentrated compositions for preparing moisturizing agents for soils comprising a depolymerized carboxymethyl cellulose, a compatibilizer and at least one surfactant.
This invention also pertains to aqueous solutions prepared from the compositions and to a method for moisturizing soils.
Plants require specific amounts of moisture to germinate, grow and remain viable. In conditions of water scarcity and/or high evapotranspiration, soil loses water rapidly due to high temperatures, low humidity, high winds and plant transpiration. Moisture in the soil is drawn to exposed soil surfaces by capillary action and lost by evaporation into the air. At the same time, moisture drawn from the soil into plant root fibers by osmosis is transpired through the plant stems and leaf systems, and that fraction not converted by photosynthesis is then lost by evaporation from pores of leaf surfaces. Under such conditions, soil volumetric water content can decrease significantly.
Moreover, irrigation water applied to coarse, sandy soils, can move past the plant root zone due to channeling, defined as the rapid movement of water downward through large pore spaces, and lack of retention, caused by lack of organic matter available to absorb available water.
Also water repellent soils present significant hydrologic and agronomic challenges. Since they are characterized by changes in the surface chemistry that impede or completely inhibit hydration, they show retarded water infiltration into the soil (leading to runoff, erosion, and leaching) and strong effects on the regular growth and maintenance of turf grass and a variety of agricultural crops.
Where there is a marked change in ground temperatures between day and night, there is a significant air inhalation into porous soils during the night-time cooling (contraction) cycle and exhalation of air and moisture in the heat of the day. This further aggravates the overall evaporative moisture loss.
Moisture is typically added to the soil by watering using manual or automatic means, such as sprinkler and drip irrigation systems. Such systems must nevertheless be connected to expensive and elaborate irrigation conduits and controls, which severely limit usage and have high energy consumption.
A further method for maintaining the ground moisture, utilizes the sponge like materials which are previously mixed with the soil surrounding the plant roots and then imbued with water during the sprinkling watering either natural or artificial. These materials usually are not biodegradable and contaminate the soils in which are inserted.
Many methods use moisturizing agents as soil additives to increase volumetric water content. The moisturizing agents are usually compositions of (co)polymers of natural, semi-synthetic or synthetic origin.
These polymer compositions are mixed into an aqueous solution or suspension and applied to the soil surface. The application can be accomplished in variety of ways, including but not limited to, spraying, casting, mulching, tilling or otherwise incorporating into the top layers of soils.
One of the polymers suitable as moisturizing agents is carboxymethyl cellulose (CMC). Carboxymethyl cellulose is able to absorb and hold water, when irrigation water is applied, and release it during irrigation intervals or dry periods.
For example, WO 2007/146055 describes a substrate, which releases impregnated water, gas and nutrients when interacting with biological organisms, comprising a mixture of a salt of carboxymethyl cellulose compound, having an average molecular weight ranging between 90,000 and 700,000, a hydrated metallic salt, water, a micro-nutrient selected from the group consisting of zinc and zinc salts, at least one plant growth additive selected from the group consisting of plant growth hormones and plant growth regulators, at least one preservative, a surfactant, and an acetic acid component selected from the group consisting of acetic acid or acetic acid salts.
U.S. Pat. No. 4,865,640 claims a substrate which gradually releases impregnated water and gas when interacting with a biological organism essentially comprising a mixture of: a) cellulosic compound ranging from 13% by weight having an average molecular weight ranging between 90,000 and 700,000 represented by the formula: R—O—COOM, in which “M” is a metal substituted for hydrogen on the carboxyl group of the cellulosic compound and “R” is cellulosic chain; b) a hydrated metallic salt ranging from 0.1-0.3% by weight; and c) water ranging from 97-99% by weight.
Sometimes, when watering process is supposed to be optimized for the growing conditions, localized dry spots (“LDS”) may take place also in the presence of a moisturizing agent. It can be caused by excessive thatch, compacted soil, poor irrigation coverage, steep sloping grade (water runoff), high soil salinity, improper chemical usage, insects, diseases and water-repellent soil. LDS is characterized by irregular, isolated, hydrophobic areas problematic in the crop or turf stand.
The number of localized dry spots caused by inhomogeneous water distribution can be minimized by adding surfactants to the moisturizing agents. In fact the surfactants acting as wetting agent allow water to spread horizontally and to penetrate to a useful depth through the small channels and capillaries of the soil without being repelled or retained mainly on the surface or in defined area.
This solution is described in WO 02/15687, which relates to soil treatment compositions comprising:
an active ingredient selected from the group consisting of a water soluble or dispersible polymer, a surfactant, and a combination of ingredients I and II; and B) the balance carriers and other adjunct ingredients.
The water soluble or dispersible polymer can be a polysaccharide and carboxymethyl cellulose is mentioned among the polysaccharides. In the Examples, three CMC with molecular weight ranging from 90,000 to 700,000 dalton are utilized. No particular effect of the molecular weight on the performances is described.
Usually the moisturizing agents, such as CMC, are directly applied on soil as aqueous solutions which are prepared at the application site. It is important that all the components of the moisturizing agents are correctly dosed and well dissolved to ensure that no under dosing or overdosing on the soil is obtained.
However, carboxymethyl cellulose can be difficult to be used in field situations and in solid form it takes a long time to dissolve, also under high shear stirring.
A good solution to this problem would be preparing a concentrated aqueous composition of carboxymethyl cellulose and surfactants which can be easily dosed and homogenized.
Unfortunately, it is difficult to combine adequate quantities of carboxymethyl cellulose and surfactants in concentrates and/or to obtain stable compositions in all cases. Furthermore, the types of surfactants will be limited to those compatible with the carboxymethyl cellulose.
Accordingly, there is still a need for a concentrated aqueous composition of carboxymethyl cellulose and a surfactant which can be easily diluted and applied, has increased efficacy on any kind of soil and can improve water usage efficiency by plants and grasses.
We have discovered that a concentrated aqueous composition of a depolymerized carboxymethyl cellulose (depolymerized CMC) and surfactants can be prepared with the help of a compatibilizer. These concentrates may contain high amounts of carboxymethyl cellulose and surfactants, are stable, pourable and can be easily diluted at the application or mixing site to prepare ready-to-use moisturizing agents.
The moisturizing agent can be applied to the soil and will reduce the losses of moisture from direct evaporation or from channelling and run-through, improves the proportion of soil moisture accessible to plants, and in certain conditions prevents or even reverses the evaporative loss from day/night movement in and out of porous soils. At the same time the presence of the surfactant allows water to properly hydrate the soil.
As far as the Applicant knows, no one has described the specific combination of depolymerized CMC, surfactant and compatibilizer of the present disclosure.
According to the invention, the expression “depolymerized CMC” defines a carboxymethyl cellulose whose weight average molecular weight has been reduced between 10,000 and 80,000 dalton through a chemical, enzymatic or physical treatment or a combination of these treatments.
According to the invention, the weight average molecular weight of CMC is determined by gel permeation chromatography (GPC) calibrated with pullulane standards.
The expression “degree of substitution” (DS) means the average number of carboxymethyl groups for each hydroglycosidic unit of the cellulose.